Connected: An Internet Encyclopedia
RFC 1123 - 5.2.3 VRFY and EXPN Commands: RFC-821 Section 3.3

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### 5.2.3 VRFY and EXPN Commands: RFC-821 Section 3.3

A receiver-SMTP MUST implement VRFY and SHOULD implement EXPN (this requirement overrides RFC-821). However, there MAY be configuration information to disable VRFY and EXPN in a particular installation; this might even allow EXPN to be disabled for selected lists.

A new reply code is defined for the VRFY command:

252 | Cannot VRFY user (e.g., info is not local), but will take message for this user and attempt delivery.

DISCUSSION:

  SMTP users and administrators make regular use of these commands for diagnosing mail delivery problems. With the increasing use of multi-level mailing list expansion (sometimes more than two levels), EXPN has been increasingly important for diagnosing inadvertent mail loops. On the other hand, some feel that EXPN represents a significant privacy, and perhaps even a security, exposure.

Next: 5.2.4 SEND, SOML, and SAML Commands: RFC-821 Section 3.4

Connected: An Internet Encyclopedia
RFC 1123 - 5.2.3 VRFY and EXPN Commands: RFC-821 Section 3.3